(AP) -- While injuries and suspensions have hit the team's highly-ranked defense, Boise State believes it has enough left to stay atop the Mountain West.

The team's latest setbacks, however, ensure the route won't be easy.

The 19th-ranked Broncos have to find a way to fill those holes quickly with a San Diego State team trying to win five in a row for the first time in 17 years visits Boise on Saturday night.

The short-handed Broncos (7-1, 4-0) have a half-game lead in the Mountain West as they try to win their first league title since joining the conference last season. Boise State, which hasn't lost since a 17-13 defeat at Michigan State in the season opener, is expected to be without cornerback Bryan Douglas]/db] (torn ACL) and starting safety [db]Lee Hightower (suspension) against the Aztecs.

Hightower (31 tackles, one interception) will be replaced in the lineup by redshirt freshman Darian Thompson (24 tackles, two interceptions), who has been used primarily on passing downs. In addition, Dextrell Simmons, who plays linebacker and defensive back, is considered day-to-day after leaving last Saturday's 45-14 win over Wyoming early with an undisclosed injury.

"At this part of the season, I think everybody's role increases," coach Chris Petersen said. "If you don't have enough guys with four games left in the season, that's how it goes."

The Broncos also lost several key defensive players down the stretch a year ago, before watching their undefeated season and conference crown slip away in a devastating loss to TCU. It's the program's only defeat in its last 72 home games.

Boise State appears to be in better shape this season with three of its four starters still available in the secondary.

Starting cornerbacks Jamar Taylor (40 tackles, two interceptions) and Jerrell Gavins lead a unit that has allowed an FBS-low two passing touchdowns and ranks 10th in passing yards with an average of 165.9. The Broncos are also fifth in the nation in scoring at 13.6 points per game, and are allowing 8.8 at home.

Boise State's secondary should present some challenges to San Diego State's Adam Dingwell, who will make his second start at quarterback after taking over when senior Ryan Katz suffered a season-ending broken ankle in a win at Nevada on Oct. 20. The sophomore threw for 231 yards and two touchdowns in last Saturday's 24-13 victory over UNLV.

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"I think he handled himself, was really under control with some maturity," Aztecs coach Rocky Long told the team's website. "I think he can be a great starting quarterback."

Dingwell is joined in the backfield by Adam Muema and [db]Walter Kazee[/db], who combined for 248 rushing yards and a touchdown last weekend. It was the second time this season both runners eclipsed 100 yards in the same game.
Muema rushed for 119 yards and two touchdowns in last season's 53-35 home loss to the Broncos, the lone meeting between the programs.

The Aztecs (6-3, 4-1) are seeking their first five-game winning streak since a six-game run in 1995, but they've won only once in their last 28 games against ranked opponents.

Although the San Diego State defense ranks near the bottom of the Mountain West against the pass (257.9 yards per game), it's first against the run, allowing an average of 125.4 yards.

That could make things tough on Boise State running back [db]D.J. Harper, who rushed for 105 yards and two touchdowns last weekend. Harper has seven rushing touchdowns over the last four games to move into fifth place on the school's career rushing touchdowns list with 34.

Broncos quarterback Joe Southwick, though, could have some opportunities to make plays downfield. He has been picked off in four straight games and hasn't thrown a TD pass in three.

"I think we're just continuing to build, from top to bottom," Southwick said.